In cast molding methods of producing ophthalmic lenses, such as contact lenses, a reaction mixture or polymerizable lens precursor composition is cured in a lens shaped cavity defined by a first mold member with a concave lens forming surface and a second mold member with a convex lens forming surface, or a female and male mold member, respectively. The mold members are typically produced by injection molding a thermoplastic polymer into mold shaped cavities. Examples of thermoplastic polymers used to make ophthalmic lens molds include non-polar thermoplastic polymers, such as polypropylene, polystyrene, and polyethylene; and polar thermoplastic polymers, such as ethylene-vinyl alcohol polymers and polyvinyl alcohol polymers. When cast molding a contact lens, after placing the polymerizable composition in the first mold member, the first and second mold members are placed together or coupled together to form a lens assembly with the lens shaped cavity therebetween. The mold assembly is then cured to polymerize the polymerizable composition, forming the polymerized lens body in the lens shaped cavity of the mold assembly.
Over the years, a number of different types of thermoplastic polymer materials, including polar and non-polar thermoplastic polymers, have been used to manufacture ophthalmic lenses using various types of polymerizable compositions and using various lens-making processes, including spin casting, lathing and cast molding.
When contact lens molds made of non-polar thermoplastic polymers such as polypropylene or polystyrene are used to cast mold silicone hydrogel contact lenses, it is known that additional measures typically need to be taken in order to make the lens surfaces ophthalmically acceptably wettable. For example, a surface treatment such as a plasma treatment can be applied to the lens surfaces as part of the manufacturing process. Alternatively, a polymeric interpenetrating network wetting agent can be incorporated into the lens body as part of the manufacturing process in order to make the lens body ophthalmically acceptably wettable.
Recently, cast molding silicone hydrogel contact lenses in molds made of highly polar thermoplastic polymers such as ethylene-vinyl alcohol (EVOH) copolymers, for example SOARLITE™ S (a polar resin of EVOH copolymers with an percent polarity of from about 10% to about 12% available from Nippon Gohsei, Ltd., Osaka, Japan) has been found to result in lenses having ophthalmically acceptably wettable surfaces. Previously, when molded using non-polar thermoplastic polymers, it was necessary to apply a surface treatment such as, for example a plasma treatment, or to include an interpenetrating network of a polymeric wetting agent in silicone hydrogel contact lenses in order for the lens surfaces to be ophthalmically acceptably wettable when hydrated. The use of contact lens molds comprising these highly polar thermoplastic polymers (i.e., thermoplastic polymers with average polarities greater than or equal to 9%, such as, for example, greater than or equal to 10%, greater than or equal to 12%, greater than or equal to 15%, etc.) made it possible to produce wettable silicone hydrogel contact lenses without the need for a surface treatment, or an interpenetrating network of a polymeric wetting agent in the lens body. However, these highly polar thermoplastic polymers such as EVOH are expensive materials, which negatively impacts production costs. Molds made of EVOH typically are harder and more brittle than would be ideal, which negatively impacts lens yields. Also, due to the high level of adhesion typically seen between EVOH molds and silicone hydrogels, after curing a silicone hydrogel contact lens body in a mold assembly of mold members comprising EVOH, separation of the mold assembly to separate the two mold members of the mold assembly typically requires a “wet” demolding process, i.e., a demolding process involving the application of a liquid to the mold assembly containing the polymerized lens body, in order to allow the two mold members to be separated, leaving the lens body remaining in contact with one and only one of the two mold members. It is believed that the high level of adhesion observed between EVOH molds and silicone hydrogels is due at least in part to the fact that EVOH is an elastomeric thermoplastic. Further, after wet demolding, the silicone hydrogel lens body may need to be exposed to an additional amount of a liquid during a “wet” delensing process in order to release the lens body from the one remaining EVOH mold member with which it remained in contact following the demolding step. Additionally, silicone hydrogel contact lenses often require the use of an organic solvent-based washing process in order for the lenses to become ophthalmically acceptably wettable, further increasing material, equipment and production costs.
US Patent Publication No. 2008/0290534 describes the desirability of using a mold having a surface energy less than 30 mN/m when the lens body is released from the mold during aqueous hydration (i.e., when the lens is wet delensed), and teaches that using a monomer or cured lens having a surface energy which is greater than the surface energy of the mold (such that the surface energy differential of the surface energy of the monomer or cured lens—the surface energy of the mold part is greater than 0) is preferred. This application discloses contact lens molds comprising a thermoplastic polymer alone or a mixture of a thermoplastic polymer and an additive, wherein the molds have a percent polarity from 0% to 1.9% and a total surface energy less from 28 mN/m to 43 mN/m.
In view of the above, it can be appreciated that a need exists for new contact lens molds having polar molding surfaces which can be used for cast molding silicone hydrogel ophthalmic lenses, particularly when using polymerizable compositions having relatively low surface tensions (e.g., a surface tension that is lower than the surface energy of the molding surface), new silicone hydrogel ophthalmic lenses cast molded using these molds and polymerizable compositions, and associated manufacturing methods that use less expensive, more process-friendly molding materials, particularly molds which can be used to dry demold and dry delens cast molded silicone hydrogel lens bodies formed from these polymerizable compositions, or which can produce silicone hydrogel lens bodies having ophthalmically acceptably wettable surfaces from these polymerizable compositions without application of a surface treatment to the lens body or the presence of an interpenetrating network (IPN) of a polymeric wetting agent in the polymerizable composition or lens body.
All publications, including patents, published patent applications, scientific or trade publications and the like, cited in this specification are hereby incorporated herein in their entirety.